Inkjet printing system and fluorinated ink

ABSTRACT

An inkjet printing system, comprising an inkjet printer and an ink composition comprising:
         (a) water;   (b) dispersed pigment particles;   (c) a humectant; and   (d) a fluorinated polyurethane additive which is different from any pigment polymeric dispersant in the ink, the additive having a weight average molecular weight of at least 10,000 daltons.

FIELD OF THE INVENTION

The invention relates generally to the field of pigmented and clear inks for ink jet printing, and in particular to inks which are useful for thermal ink jet printing. More specifically, the invention relates to pigmented and clear inks for high-speed thermal inkjet printing which result in durable images.

BACKGROUND OF THE INVENTION

Ink jet printing is a non-impact method for producing printed images by the deposition of ink droplets in a pixel-by-pixel manner to an image-recording element in response to digital signals. There are various methods that may be utilized to control the deposition of ink droplets on the image-recording element to yield the desired printed image. In one process, known as drop-on-demand ink jet, individual droplets are projected as needed onto the image-recording element to form the desired printed image. Common methods of controlling the ejection of ink droplets in drop-on-demand printing include thermal bubble formation (thermal ink jet (TIJ)) and piezoelectric transducers. In another process known as continuous ink jet (CIJ), a continuous stream of droplets is generated and expelled in an image-wise manner onto the surface of the image-recording element, while non-imaged droplets are deflected, caught, and recycled to an ink sump. Ink jet printers have found broad applications across markets ranging from desktop document and photographic-quality imaging, to short run printing and industrial labeling.

Ink compositions containing colorants used in ink jet printers can be classified as either pigment-based, in which the colorant exists as pigment particles suspended in the ink composition, or as dye-based, in which the colorant exists as a fully solvated dye species that consists of one or more dye molecules. Pigments are highly desirable since they are far more resistant to fading than dyes. However, pigment-based inks have a number of drawbacks. Great lengths must be undertaken to reduce a pigment particle to a sufficiently small particle size and to provide sufficient colloidal stability to the particles. Pigment-based inks often require a lengthy milling operation to produce particles in the sub-micron range needed for most modern ink applications. If the pigment particles are too large light scattering can have a detrimental effect on optical density and gloss in the printed image.

A second drawback of pigmented inks is their durability after printing, especially under conditions where abrasive forces have been applied to the printed image. Pigment-based inks typically reside at the surface of the imaging receiver to which they are printed and this makes the printed images particularly susceptible to abrasive forces. To this extent, pigmented inks have been formulated with various polymers, dispersants and other addenda to provide durable images that can withstand post printing physical abuse and environmental conditions.

The degree of abrasion resistance of a printed image is also a function of time after printing. At short time intervals after printing, typically from a few minutes to a few hours, the ink undergoes several complex dynamic changes. As the ink contacts the receiver, some of the components penetrate into the receiver and the droplets can simultaneously spread laterally on the receiver surface. Carrier fluids such as water and humectants are drawn into the receiver by capillary forces and the polymer binders begin to film form. At short time intervals the binder film formation is incomplete and the resulting pigment cake is particularly susceptible to abrasive forces. Typically, the more total fluid that is printed to the receiver (and hence more water) the longer it takes for the ink to dry and form a durable image. The abrasion resistance of the image is further affected by the presence of humectants, which are necessary for optimal firing performance, but which are retained in the pigment cake for some period of time. Since most humectants have much lower vapor pressures than water, they are relatively slow to evaporate and can be retained in the image receiver for several hours. Humectants can have the effect of plasticizing the polymer binder and making the surface of the image tacky or softer than if no humectant was present. Once the humectants evaporate the resulting pigment cake, consisting primarily of pigment and binders, reaches a steady state composition, and determines the long-term abrasion resistance of the printed image.

Images printed from an ink jet printer are also susceptible to abrasive forces as the image receiver is advanced through the printer. Typically, there is some mechanical means for advancing the print past the printhead and out of the printer. In some designs a spur wheel is used to advance the printed receiver. Spur wheels are often made from a hard plastic or metal and have the shape of a disk with points or spurs located on the periphery of the wheel. The spurs contact the printed receiver and can physically penetrate the uppermost area of the printed image leaving behind a small hole. In extreme cases the spurs can plow into the receiver and tear off small sections of the imaged areas. In either case, the mechanical abrasion caused by the spur wheel occurs at short time intervals on the order of a few seconds after printing and results in a defect that is objectionable to the eye.

Pigmented inks for ink jet printing have been formulated with acrylic polymers; however, the acrylic polymers alone are insufficient in providing durable images that resist scratches and other forms of physical abuse. A second class of polymers that have been used as abrasion resistance additives in pigment-based inks are the polyurethanes, or urethane resins as they are sometimes called. U.S. Pat. No. 6,136,890 discloses a pigment-based ink jet ink wherein the pigment particles are stabilized by a polyurethane dispersant. US Publication No. 2004/0242726 discloses a pigment dispersed by a cross-linking step between a resin having a urethane bond and a second water-soluble polymer.

Although polyurethanes are known for their excellent abrasion resistance, they also have a number of drawbacks. For example, not all polyurethane polymers are conducive to jetting from a thermal ink jet head. In particular, water-dispersible polyurethane particles, such as those disclosed in U.S. Pat. Nos. 6,533,408 and 6,268,101, Statutory Invention Registration No. US H2113H, and US Publication Numbers 2004/0130608 and 2004/0229976 are particularly difficult to jet from a thermal inkjet printhead at high firing frequencies. It is highly desirable to fire inks at high firing frequencies from an inkjet printer since this is one variable that controls the speed at which the image can be printed.

Another way to improve the abrasion resistance of a printed image is to apply a clear ink as an overcoat to the image. The clear inks, also known as overcoat solutions or colorless ink compositions, are typically formulated with polymer, water, and other components commonly used in aqueous-based ink jet ink formulations, for example, humectants, organic solvents, surfactants, and biocides. US Publication Numbers 2006/0100306 and 2006/0100308 disclose the use of polyurethanes and mixtures of polyurethanes and acrylic polymers having specified acid numbers for use in clear ink compositions; however, clear inks formulated with polyurethanes also suffer from the same short term durability issues as colored inks since they have many components in common with their colored ink counterparts. In addition, the application of a clear ink increases the total amount of water applied to the receiver and therefore slows down the drying of the imaged area of the prints. Although the application of clear ink can improve the long term durability, its application can adversely affect the short term durability due to the increased water load on the receiver.

Both pigment and clear inks can be difficult to jet through ink jet printheads having small nozzle diameters especially by the thermal ink jet printing process. In recent years, thermal ink jet printers have moved to higher jetting frequencies and smaller nozzle diameters to provide faster printing speeds with higher image quality. Thermal ink jet printers are now capable of printing (in drop volumes of 3 picoliters or less) at jetting frequencies in excess of 10 kHz and the need for higher velocity firings is a highly desirable feature. However, this high frequency firing often comes at the cost of variability in the firing velocity, which leads to poor image quality in the final printed image. In addition, the demands of current thermal ink jet printing requires that the nozzles fire for a large number of firings during the life-time of a printer. As an example, a typical ink jet nozzle may be required to fire in excess of 5×10⁷, and up to as many as 1×10⁹, individual firing events without malfunctioning or ceasing to fire altogether.

Although polyurethane binders have found use in inkjet inks there remains the need to provide both pigment-based and clear inks capable of providing durable images and which satisfy the demands of high frequency thermal ink jet printing. It is therefore an object of this invention to provide pigment-based inks and clear inks for inkjet printing whereby, the pigment-based inks and/or a clear ink contain an aqueous polyurethane binder that provides abrasion resistance to an image at both short time and long time intervals after printing and which can be jetted at high firing frequencies from an inkjet printhead.

SUMMARY OF THE INVENTION

The invention provides an inkjet printing system, comprising an inkjet printer and an ink composition comprising:

(a) water;

(b) dispersed pigment particles;

(c) a humectant; and

(d) a fluorinated polyurethane additive which is different from any pigment polymeric dispersant in the ink, the additive having a weight average molecular weight of at least 10,000 daltons.

The invention also provides an inkjet ink, an inkjet ink set, and a method of printing comprising jetting the ink jet ink onto a recording element.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the present invention will become more apparent when taken in conjunction with the following description and drawings wherein identical reference numerals have been used, where possible, to designate identical features that are common to the figures, and wherein the FIGURE is a schematic view of an inkjet printer system of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The ink jet inks of the present invention are aqueous-based inks. “Aqueous-based” is defined herein to mean the ink comprises mainly water as the carrier medium for the remaining ink components. In a preferred embodiment, the inks of the present invention comprise at least about 50 weight percent water. Pigment-based inks are defined as inks containing at least a dispersion of water-insoluble pigment particles. A clear ink in the present invention is defined as an ink composition that does not contain colorants, including colored pigments or colored dyes. The clear ink is typically aqueous based and can contain humectants and polymers used in the art of inkjet printing. The clear ink can be slightly colored due to the presence of humectants, polymers, or impurities, but is not intentionally colored by the addition of a colorant.

An ink set is defined as a set of two or more inks. An ink set may contain pigment-based inks of different colors, for example, cyan, magenta, yellow, red, green, blue, orange, violet, or black. In one embodiment, a carbon black pigmented ink is used in an ink set comprising at least three inks having separately, a cyan, a magenta, and a yellow colorant. Useful ink sets also include, in addition to the cyan, magenta, and yellow inks, complimentary colorants such as red, blue, violet, orange, or green inks. In addition, the ink set may comprise light and dark colored inks, for example, light cyan and light magenta inks commonly used in the ink sets of wide format printers. It is possible to include one or more inks that comprise a mixture of different colored pigments in the ink set. An example of this is a carbon black pigment mixed with one or more colored pigments or a combination of different colored pigments. An ink set may also include one or more pigment-based inks in combination with one or more clear inks. An ink set may also include at least one or more pigment-based inks in combination with additional inks that are dye-based ink. An ink set may further comprise one or more inks containing a self-dispersing carbon black pigment ink which is used primarily for printing of text and a plurality of cyan, magenta, yellow, and black inks which are used primarily for photographic quality printing.

Ink compositions of the present invention comprise at least one water-dispersible polyurethane compound. “Water-dispersible” is defined herein to mean individual polymer molecules or colloidal assemblies of polymer molecules which are stably dispersed in the ink without the need for a dispersing agent. Water dispersible polyurethanes employed in the present invention have the general formula of (I)

wherein R₁ in the structure (I) above is the central portion of the monomer unit that is the polymerization product of a diisocyanate; X—R₂—X represents a soft segment comprising at least fluoralkyl or fluorinated polyether groups; R₃ is the central portion of a unit containing an acid group; and X and Y can be the same or different and are —O— or —N— atom.

R₁ is typically a hydrocarbon group having a valence of two, more desirably containing a substituted or unsubstituted alicyclic, aliphatic, or aromatic group, preferably represented by one or more of the following structures:

X—R₂—X defines a first soft segment of the polyurethane and desirably represents a fluorinated prepolymer comprising fluorinated side chains. Useful fluorinated side chains include fluoroalkyls and fluorinated polyethers. The fluorinated soft segment, X—R₂—X, is introduced into the polyurethane backbone by using a prepolymer with both ends terminated with a hydroxyl (diol) or an amino (diamine) group. The prepolymer having terminal hydroxyl groups is known as a polyol, and that having terminal amine groups is known as a polyamine.

Exemplary polyether diols having fluorinated side chains useful for forming X—R₂—X include those having the generic structural Formula II:

where X is hydrogen or alkyl, R is alkyl having from 2 to 5 carbons, y is 0 to 2, z is 0 to 8, and n is 4 to 20.

Polyether polyols having fluorinated side chains greater than 6 carbons can be used in the present invention, but are less desirable since longer chain perfluro alcohols can degrade into pefluoroctanoic acid and other long chain fluorocarboxylic acids, which are known to have environmental concerns. Particularly useful polyether polyols having fluorinated side chains are those having between 2 and 6 carbon atoms and are exemplified by structural Formulas IIa and IIb, where n is from about 4 to about 20. Desirably, the polyether polyol having fluorinated side chains has 2 to 4 carbon atoms.

Useful polyether polyols having fluorinated side chains are sold under the trade name POLYFOX® fluorosurfactant diols (Omnova Solutions).

Another useful group for forming the first soft segment X—R₂—X is a silanol terminated polytrifluoroalkyl methylsiloxane having the generic structural Formula III, where m is from 2 to 10 and n is from 1 to 8:

Particularly useful fluorinated silanol terminated polyfluoroalkylmethylsiloxanes are those with a fluoroalkyl group having between 2 and 4 carbon atoms. Examples of silanol terminated polytrifluoropropylmethylsiloxanes (n=1 in Formula III) useful in the invention are commercially available as FMS-9921 (Mw 550-800) and FMS-9922 (Mw 800-1200) from Gelest, Inc.

The first soft segment is present in the polyurethane of the present invention at from 0.2% to 30% by weight, more typically from 0.2% to 20% and desirably from 0.2% to 10% based on the total weight of the polymer.

X—R₂—X can also be a mixture of a first fluorinate soft segment and a second non-fluorinated soft segment selected from, a polyether polyol, polyester polyol, polycarbonate polyol, polydimethyl siloxane diol, polyether diamine, polyester diamine, polycarbonate diamine, or aminoalkyl terminated polydimethyl siloxane. Useful polyether diols and diamines are those sold under the trade name TERATHANE® from Dupont and trade name JEFFAMINE® D, ED, and M series from Huntsman. A particularly useful polyether polyol useful for forming the second soft segment is tetramethylene glycol and can desirably have a molecular weight between 600 and 2500. A particularly useful polyether diamine is a bis(3-aminopropyl) terminated polytetrahydrofuran having a molecular weight between 600 and 2000.

Another particularly useful second soft segment for the polyurethane is a polydimethylsiloxane diol or aminoalkyl terminated polydimethyl siloxane. Polyurethanes prepared from a mixture of fluorinated soft segments and polydimethylsiloxane soft segments can provide improved durability to the printed image especially with respect to spur wheel defects. A particularly useful polyurethane contains a mixture of a first soft segment formed from a diol having fluorinated polyether side chains and a second soft segment formed from an aminoalkyl terminated polydimethyl siloxane. Another particularly useful polyurethane contains a mixture of a first soft segment having polytrifluoropropylmethylsiloxanes groups and a second soft segment having polyether groups. Desirably, the polyether groups are polytetramethylene oxides.

The second soft segment comprising polyether, polyester, polydimethyl siloxane, polycarbonate polyol, or polyamine can be present in the polyurethane at from 0.2% to 30% by weight, more typically from 0.2% to 20%, and desirably from 0.2% to 10% based on the total weight of the polymer.

R₃ is preferably the central portion of a monomeric unit containing a phosphoric acid, carboxylic acid, or sulfonic acid group, most preferably being carboxylic acids, such as 2,2′-bis(hydroxymethyl)propionic acid, 2,2′-bis(hydroxymethyl)butyric acid, and hydroxyethylether of 4,4′-bis(4-hydroxyphenyl)valeric acid.

Conventional processes of making polyurethane dispersions involve the steps of preparing a prepolymer having a relatively low molecular weight and a small excess of isocyanate groups and chain-extending with a chain extender the prepolymers into a high molecular weight polyurethane during the dispersion process. Besides the raw materials the polyurethane dispersions sold by various manufactures differs in the process used to prepare the prepolymers (e.g. Solvent free prepolymer process, Ketimine and Ketazine process, Hybrid system, and Ethyl acetate process), and the type of chain extender used in the dispersion step. Such materials and processes have been disclosed in, for example, U.S. Pat. No. 4,335,029; in “Aqueous Polyurethane Dispersions,” by B. K. Kim, Colloid & Polymer Science, Vol. 274, No. 7 (1996) 599-611 © Steinopff Verlag 1996; and in “Polyurethane Dispersion Process,” by Manea et al., Paint and Coating Industry, January 2007, Page 30.

The polyurethane dispersions useful for the practice of this invention are desirably to be prepared without involving the chain-extension step during the dispersion step. Instead it prefers to have the chemical reaction for forming urethane or urea linkages completed prior to the dispersion step. This will insure that the polyurethane dispersions used in the ink compositions of the invention have well-controlled molecular weight and molecular weight distribution and be free of gel particles.

In one particularly useful processes the polyurethane used in the present invention is prepared in a water miscible organic solvent such as tetrahydrofuran, followed by neutralizing the hydrophilic groups, e.g. carboxylic acid groups, with an aqueous inorganic base, e.g. potassium hydroxide solution. The polyurethane solution is then diluted with doubly distilled de-ionized water. Finally the water miscible organic solvent is removed by distillation to form stable polyurethane dispersions. In this process the polyurethane particles are formed by precipitation during solvent evaporation.

In a second desirable process the polyurethane useful for the invention is prepared in a water immiscible organic solvent, e.g. ethyl acetate. The polyurethane is neutralized with an aqueous inorganic base and water is added to form an aqueous dispersion comprising primarily minute drops of polyurethane-water immiscible organic solvent solution suspended in water. The water immiscible organic solvent is then removed to form the desired polyurethane dispersion.

In another desirable process the polyurethane is formed by a sequential polymerization process where a soft polyurethane segment is formed first by reacting a diisocyanate compound with a fluorinated polyether diol or diamine. The soft polyurethane segment then reacts further with a mixture of diisocyanate compound, a fluorinated polyether polyol, and a low molecular weight diol having a hydrophilic group, e.g. a carboxylic acid group.

The polyurethane of this invention has a sufficient amount of acid groups in the molecule to make the polymer usable in an aqueous based ink. In one embodiment the polyurethane has an acid number of greater than or equal to 20. In order to achieve optimal jetting from an inkjet printhead the acid number is typically from 50 to 160, more usefully from 60 to 160, and more desirably from 60 to 130. The acid number is defined as the milligrams of potassium hydroxide required to neutralize one gram of dry polymer. The acid number of the polymer may be calculated by the formula given in the following equation: Acid number=(moles of acid monomer)*(56 grams/mole)*(1000)/(total grams of monomers) where, moles of acid monomer is the total moles of all acid group containing monomers that comprise the polymer, 56 is the formula weight for potassium hydroxide, and total grams of monomers is the summation of the weight of all the monomers, in grams, comprising the target polymer.

The acid groups on the polyurethane compounds of the present invention are at least partially neutralized (converted into salts) using monovalent inorganic base, preferably an alkaline metal hydroxide selected from the group of potassium hydroxide, sodium hydroxide, rubidium hydroxide, or lithium hydroxide. In a preferred embodiment, at least 70 percent of the available acid groups on the polymer are converted into salts using inorganic base, more preferably, at least 90% of the available acid groups are converted. From a manufacturing perspective, preferably less than 100% of the acid groups are neutralized as this can lead to lack of control of the pH of the inks.

The polyurethane of this invention has a minimum weight average molecular weight of at least 10,000 daltons. Desirably, the polyurethane has a maximum weight average molecular weight of 150,000. Polyurethanes having molecular weights less than or equal 10,000 provide insufficient durability and often exhibit poor jetting performance. Molecular weights above 150,000 have negative impacts on the relatively low viscosity requirements of an inkjet ink which are desirably jetted at high frequencies and with low variability. More typically the molecular weight of polyurethane is from 20,000 to 100,000, most desirably from 20,000 to 50,000.

The polyurethane used in the invention is present in the ink jet ink at amounts between 0.1% and 5% by weight based, more desirably from 0.1% to 2%, and in one particular embodiment between 0.5% and 2% based on the total ink composition.

The polyurethane dispersions useful for the practice of this invention typically have a mean particle size of less than 100 nm, and more desirably less than 50 nm.

In one exemplary embodiment, an ink composition comprises a first polyurethane comprising fluorinated side chains and a second non-fluorinated polyurethane. Ink compositions can comprise a mixture of a fluorinated polyurethane comprising fluorinated side chains and a second non-fluorinated polyurethane comprising soft segments having polyether, polyester, polycarbonate, polydimethylsiloxane, or polycaprolactone groups. The addition of a second non-flourinated polyurethane to an ink composition comprising a fluorinated polyurethane can have the advantage of improving the jetting velocity and jetting velocity variation of the fluorinated polyurethane-based ink composition. In a particularly useful embodiment, both the fluorinated and non-fluorinated polyurethanes have an acid number from 60 to 150. Useful ratios of fluorinated polyurethane to non-fluorinated polyurethane can be from 10:1 to 100:1 on a weight basis. The jetting behavior of ink compositions comprising polymerically dispersed pigment particles and fluorinated polyurethanes can be significantly improved with the addition of greater than or equal to 1 weight % of a non-fluorinated polyurethane based on the total polyurethane load in the ink composition.

Unless otherwise specifically stated, use of the term “substituted” or “substituent” means any group or atom other than hydrogen. Additionally, when the term “group” is used, it means that when a substituent group contains a substitutable hydrogen, it is also intended to encompass not only the substituent's unsubstituted form, but also its form further substituted with any substituent group or groups as herein mentioned, so long as the substituent does not destroy properties necessary for device utility. Suitably, a substituent group may be halogen or may be bonded to the remainder of the molecule by an atom of carbon, silicon, oxygen, nitrogen, phosphorous, sulfur, selenium, or boron. The substituent may be, for example, halogen, such as chloro, bromo or fluoro; nitro; hydroxyl; cyano; carboxyl; or groups which may be further substituted, such as alkyl, including straight or branched chain or cyclic alkyl, such as methyl, trifluoromethyl, ethyl, t-butyl, 3-(2,4-di-t-pentylphenoxy) propyl, and tetradecyl; alkenyl, such as ethylene, 2-butene; alkoxy, such as methoxy, ethoxy, propoxy, butoxy, 2-methoxyethoxy, sec-butoxy, hexyloxy, 2-ethylhexyloxy, tetradecyloxy, 2-(2,4-di-t-pentylphenoxy)ethoxy, and 2-dodecyloxyethoxy; aryl such as phenyl, 4-t-butylphenyl, 2,4,6-trimethylphenyl, naphthyl; aryloxy, such as phenoxy, 2-methylphenoxy, alpha- or beta-naphthyloxy, and 4-tolyloxy; carbonamido, such as acetamido, benzamido, butyramido, tetradecanamido, alpha-(2,4-di-t-pentyl-phenoxy)acetamido, alpha-(2,4-di-t-pentylphenoxy)butyramido, alpha-(3-pentadecylphenoxy)-hexanamido, alpha-(4-hydroxy-3-t-butylphenoxy)-tetradecanamido, 2-oxo-pyrrolidin-1-yl, 2-oxo-5-tetradecylpyrrolin-1-yl, N-methyltetradecanamido, N-succinimido, N-phthalimido, 2,5-dioxo-1-oxazolidinyl, 3-dodecyl-2,5-dioxo-1-imidazolyl, and N-acetyl-N-dodecylamino, ethoxycarbonylamino, phenoxycarbonylamino, benzyloxycarbonylamino, hexadecyloxycarbonylamino, 2,4-di-t-butylphenoxycarbonylamino, phenylcarbonyl amino, 2,5-(di-t-pentylphenyl)carbonylamino, p-dodecyl-phenylcarbonylamino, p-tolylcarbonylamino, N-methylureido, N,N-dimethylureido, N-methyl-N-dodecylureido, N-hexadecylureido, N,N-dioctadecylureido, N,N-dioctyl-N′-ethylureido, N-phenylureido, N,N-diphenylureido, N-phenyl-N-p-tolylureido, N-(m-hexadecylphenyl)ureido, N,N-(2,5-di-t-pentylphenyl)-N′-ethylureido, and t-butylcarbonamido; sulfonamido, such as methylsulfonamido, benzenesulfonamido, p-tolylsulfonamido, p-dodecylbenzenesulfonamido, N-methyltetradecylsulfonamido, N,N-dipropyl-sulfamoylamino, and hexadecylsulfonamido; sulfamoyl, such as N-methylsulfamoyl, N-ethylsulfamoyl, N,N-dipropylsulfamoyl, N-hexadecylsulfamoyl, N,N-dimethylsulfamoyl, N-[3-(dodecyloxy)propyl]sulfamoyl, N-[4-(2,4-di-t-pentylphenoxy)butyl]sulfamoyl, N-methyl-N-tetradecylsulfamoyl, and N-dodecylsulfamoyl; carbamoyl, such as N-methylcarbamoyl, N,N-dibutylcarbamoyl, N-octadecylcarbamoyl, N-[4-(2,4-di-t-pentylphenoxy)butyl]carbamoyl, N-methyl-N-tetradecylcarbamoyl, and N,N-dioctylcarbamoyl; acyl, such as acetyl, (2,4-di-t-amylphenoxy)acetyl, phenoxycarbonyl, p-dodecyloxyphenoxycarbonyl methoxycarbonyl, butoxycarbonyl, tetradecyloxycarbonyl, ethoxycarbonyl, benzyloxycarbonyl, 3-pentadecyloxycarbonyl, and dodecyloxycarbonyl; sulfonyl, such as methoxysulfonyl, octyloxysulfonyl, tetradecyloxysulfonyl, 2-ethylhexyloxysulfonyl, phenoxysulfonyl, 2,4-di-t-pentylphenoxysulfonyl, methylsulfonyl, octylsulfonyl, 2-ethylhexylsulfonyl, dodecylsulfonyl, hexadecylsulfonyl, phenylsulfonyl, 4-nonylphenylsulfonyl, and p-tolylsulfonyl; sulfonyloxy, such as dodecylsulfonyloxy, and hexadecylsulfonyloxy; sulfinyl, such as methylsulfinyl, octylsulfinyl, 2-ethylhexylsulfinyl, dodecylsulfinyl, hexadecylsulfinyl, phenylsulfinyl, 4-nonylphenylsulfinyl, and p-tolylsulfinyl; thio, such as ethylthio, octylthio, benzylthio, tetradecylthio, 2-(2,4-di-t-pentylphenoxy)ethylthio, phenylthio, 2-butoxy-5-t-octylphenylthio, and p-tolylthio; acyloxy, such as acetyloxy, benzoyloxy, octadecanoyloxy, p-dodecylamidobenzoyloxy, N-phenylcarbamoyloxy, N-ethylcarbamoyloxy, and cyclohexylcarbonyloxy; amine, such as phenylanilino, 2-chloroanilino, diethylamine, dodecylamine; imino, such as 1 (N-phenylimido)ethyl, N-succinimido or 3-benzylhydantoinyl; phosphate, such as dimethylphosphate and ethylbutylphosphate; phosphite, such as diethyl and dihexylphosphite; a heterocyclic group, a heterocyclic oxy group or a heterocyclic thio group, each of which may be substituted and which contain a 3 to 7 membered heterocyclic ring composed of carbon atoms and at least one hetero atom selected from the group consisting of oxygen, nitrogen, sulfur, phosphorous, or boron. Such as 2-furyl, 2-thienyl, 2-benzimidazolyloxy or 2-benzothiazolyl; quaternary ammonium, such as triethylammonium; quaternary phosphonium, such as triphenylphosphonium; and silyloxy, such as trimethylsilyloxy.

If desired, the substituents may themselves be further substituted one or more times with the described substituent groups. The particular substituents used may be selected by those skilled in the art to attain desirable properties for a specific application and can include, for example, electron-withdrawing groups, electron-donating groups, and steric groups. When a molecule may have two or more substituents, the substituents may be joined together to form a ring such as a fused ring unless otherwise provided. Generally, the above groups and substituents thereof may include those having up to 48 carbon atoms, typically 1 to 36 carbon atoms and usually less than 24 carbon atoms, but greater numbers are possible depending on the particular substituents selected.

Ink compositions, both pigment-based and clear, can comprise polyurethanes of the present invention at levels from 0.1 to 10% by weight based on the total ink components. More desirable abrasion resistance can be imparted to the inkjet images when the ink composition contains from 0.5 to 10% by weight of inventive polyurethane. In one particular embodiment the polyurethane is present in the ink composition at from 0.5 to 3%. These ranges of polyurethane provide excellent jetting of the ink composition from the printhead while minimizing viscosity effects that could affect jetting performance.

The pigment particles that are useful in the invention may be prepared by any method known in the art of inkjet printing. Useful methods commonly involve two steps: (a) a dispersing or milling step to break up the pigments to primary particles, where primary particle is defined as the smallest identifiable subdivision in a particulate system, and (b) a dilution step in which the pigment dispersion from step (a) is diluted with the remaining ink components to give a working strength ink.

The milling step (a) is carried out using any type of grinding mill such as a media mill, a ball mill, a two-roll mill, a three-roll mill, a bead mill, and air-jet mill, an attritor, or a liquid interaction chamber. In the milling step (a), pigments are optionally suspended in a medium that is typically the same as or similar to the medium used to dilute the pigment dispersion in step (b). Inert milling media are optionally present in the milling step (a) in order to facilitate break up of the pigments to primary particles. Inert milling media include such materials as polymeric beads, glasses, ceramics, metals and plastics as described, for example, in U.S. Pat. No. 5,891,231. Milling media are removed from either the pigment dispersion obtained in step (a) or from the ink composition obtained in step (b).

A dispersant is present in the milling step (a) in order to facilitate break up of the pigments into primary particles. For the pigment dispersion obtained in step (a) or the ink composition obtained in step (b), a dispersant is present in order to maintain particle stability and prevent settling. The dispersant for the pigment particles can be a surfactant, such as for example, potassium oleylmethyl taurate (KOMT), sodium dodecyl sulfate or sodium dioctyl sulfosuccinate.

Polymeric dispersants can be used to disperse the pigment particles prior to, or during the milling step. Typically, these polymeric dispersants are copolymers made from hydrophobic and hydrophilic monomers. Examples of polymeric dispersants for pigment particles include random and block copolymers having hydrophilic and hydrophobic portions; see for example, U.S. Pat. Nos. 4,597,794, 5,085,698, 5,519,085, 5,272,201, 5,172,133, 6,043,297 and PCT Patent Publication Number WO 2004/111140A1; and graft copolymers; see for example, U.S. Pat. Nos. 5,231,131, 6,087,416, 5,719,204, or 5,714,538. Among these polymeric dispersants anionic polymeric dispersants are especially useful.

Polymeric dispersants useful for dispersing the pigment particles of the present invention are not limited in the arrangement of the monomers comprising the dispersant. The arrangement of monomers may be totally random, or they may be arranged in blocks such as AB or ABA wherein, A is the hydrophobic monomer and B is the hydrophilic monomer. In addition, the polymer may take the form of a random terpolymer or an ABC tri-block wherein, at least one of the A, B and C blocks is chosen to be the hydrophilic monomer and the remaining blocks are hydrophobic blocks dissimilar from one another.

Polymeric dispersants useful for dispersing the pigment particles can be selected from acrylics and styrene-acrylics. Styrene-acrylic polymeric dispersants especially useful in the present invention are copolymers of styrenic monomers and carboxylate monomers. Examples of such dispersants include copolymers of styrene and/or alphamethyl styrene and acrylic acid and/or methacrylic acid (such as the JONCRYL® BASF or TRUDOT® Mead Westvaco polymers) or styrene maleic anhydride and styrene maleic anhydride amic acid copolymers (such as SMA-1440, SMA-17352, SMA-1000, SMA-2000® Sartomer Inc.).

Acrylic polymeric dispersants useful in the present invention are typically formed from one or more acrylic monomer and one or more ionizable monomer, such as, for example carboxyalted or sulfonated monomers. Acrylic polymeric dispersants are typically formed from one or more hydrophobic acrylate monomer including, for example, methylmethacrylate, ethylmethacrylate, butylmethacrylate, hexylmethacryate, octylmethacrylate and decylmethacrylate.

Other especially useful polymeric dispersants are those where the hydrophobic monomer is selected from benzyl methacrylate or acrylate, or from acrylic acid esters containing an aliphatic chain having twelve or more carbons and where the hydrophilic monomer is a carboxylated monomer. Examples of acrylic acid esters having twelve or more carbons include; lauryl acrylate, lauryl methacrylate, tridecyl acrylate, tridecyl methacrylate, tetradecyl acrylate, tetradecyl methacrylate, cetyl acrylate, iso-cetyl acrylate, stearyl methacrylate, iso-stearyl methacrylate, stearyl acrylate, stearyl methacrylate, decyltetradecyl acrylate, decyltetradecyl methacrylate. Preferably the methacrylate or acrylate monomer is stearyl or lauryl methacrylate or acrylate. The hydrophobic portion of the polymer may be prepared from one or more of the hydrophobic monomers. Desirable carboxylated hydrophilic monomers are acrylic acid or methacrylic acid, or combinations thereof.

Typically, the weight average molecular weight of the polymeric dispersant has an upper limit such that it is less than 50,000 Daltons. Desirably the weight average molecular weight of the copolymer is less than 25,000 Daltons; more desirably it is less than 15,000 and most desirably less than 10,000 Daltons. The copolymer dispersants preferably have a weight average molecular weight lower limit of greater than 500 Daltons.

In one exemplary embodiment, the pigment particles are dispersed with a copolymer where the hydrophobic monomer is benzyl methacrylate and is present from 50 weight percent to 80 weight percent relative to the total weight of the polymeric dispersant and the hydrophilic monomer is methacrylic acid.

In a second embodiment, copolymer dispersants are employed which comprise a hydrophobic monomer having a carbon chain length of greater than or equal to 12 carbons present in an amount of at least 10% by weight of the total copolymer, and more desirably greater than 20% by weight, an optional additional hydrophobic monomer comprising an aromatic group and a hydrophilic monomer that is methacrylic acid. For example, the additional aromatic group containing monomer may be benzyl acrylate or benzyl methacrylate. An especially useful additional monomer is benzyl methacrylate.

The total amount of hydrophobic monomers, comprising the monomer having a chain with greater than or equal to 12 carbons and optionally, monomer containing an aromatic group, may be present in the polymer in an amount of 20 to 95% by weight of the total polymer. The hydrophobic aromatic-group containing monomer may be present in an amount from about 0 to 85% by weight of the total polymer, more typically from about 0 to 60%, and desirably from about 0 to 50%. A particularly useful embodiment of a polymeric dispersant for the pigment particles is a terpolymer of benzyl methacrylate, stearyl methacrylate and methacrylic acid. Particularly useful polymeric pigment dispersants are further described in United States Patent Application Numbers 2006/0012654 and 2007/0043144.

Encapsulating type polymeric dispersants and polymeric dispersed pigments thereof can also be used in the invention. Specific examples are described in U.S. Pat. Nos. 6,723,785, 6,852,777, and United States Patent Application Numbers 2004/0132942, 2005/0020731, 2005/00951, 2005/0075416, 2005/0124726, 2004/007749, and 2005/0124728. Encapsulating type polymeric dispersants can be especially useful because of their high dispersion stability on keeping and low degree of interaction with ink components. Composite colorant particles having a colorant phase and a polymer phase are also useful in aqueous pigment-based inks of the invention. Composite colorant particles are formed by polymerizing monomers in the presence of pigments; see for example, United States Patent Application Numbers 2003/0199614, 2003/0203988, or 2004/0127639. Microencapsulated-type pigment particles are also useful and consist of pigment particles coated with a resin film; see for example U.S. Pat. No. 6,074,467.

The pigment dispersions useful in pigment-based ink compositions of the present invention desirably have a median particle diameter of less than 200 nm and more desirably less than 100 nm. In a particularly useful embodiment, 90 percent of the weight of the pigment particles in the distribution have a diameter less than 100 nm and desirably less than 80 nm.

The polymeric dispersant (copolymer) for the pigment is not limited in the arrangement of the monomers comprising the copolymer. The arrangement of monomers may be totally random, or they may be arranged in blocks such as AB or ABA wherein, A is the hydrophobic monomer and B is the hydrophilic monomer. In addition, the polymer make take the form of a random terpolymer or an ABC tri-block wherein, at least one of the A, B, and C blocks is chosen to be the hydrophilic monomer and the remaining blocks are hydrophobic blocks dissimilar from one another.

Self-dispersing pigments useful for the practice of the invention are those that have been subjected to a surface treatment such as oxidation/reduction, acid/base treatment, or functionalization through coupling chemistry. The surface treatment can render the surface of the pigment with anionic, cationic or non-ionic groups. Examples of self-dispersing type pigments include, but are not limited to, CAB-O-JET® 200 and CAB-O-JET® 300 (Cabot Corp.), BONJET® Black CW-1, CW-2, and CW-3 (Orient Chemical Industries, Ltd.) and AQUA BLACK® 162 and 001 (Tokai Carbon, Ltd.).

Pigments suitable for use in the invention include, but are not limited to, azo pigments, monoazo pigments, disazo pigments, azo pigment lakes, β-Naphthol pigments, Naphthol AS pigments, benzimidazolone pigments, disazo condensation pigments, metal complex pigments, isoindolinone and isoindoline pigments, polycyclic pigments, phthalocyanine pigments, quinacridone pigments, perylene and perinone pigments, thioindigo pigments, anthrapyrimidone pigments, flavanthrone pigments, anthanthrone pigments, dioxazine pigments, triarylcarbonium pigments, quinophthalone pigments, diketopyrrolo pyrrole pigments, titanium oxide, iron oxide, and carbon black.

Typical examples of organic pigments that may be used include Color Index (C. I.) Pigment Yellow 1, 2, 3, 5, 6, 10, 12, 13, 14, 16, 17, 62, 65, 73, 74, 75, 81, 83, 87, 90, 93, 94, 95, 97, 98, 99, 100, 101, 104, 106, 108, 109, 110, 111, 113, 114, 116, 117, 120, 121, 123, 124, 126, 127, 128, 129, 130, 133, 136, 138, 139, 147, 148, 150, 151, 152, 153, 154, 155, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 179, 180, 181, 182, 183, 184, 185, 187, 188, 190, 191, 192, 193, 194; C. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 21, 22, 23, 31, 32, 38, 48:1, 48:2, 48:3, 48:4, 49:1, 49:2, 49:3, 50:1, 51, 52:1, 52:2, 53:1, 57:1, 60:1, 63:1, 66, 67, 68, 81, 95, 112, 114, 119, 122, 136, 144, 146, 147, 148, 149, 150, 151, 164, 166, 168, 169, 170, 171, 172, 175, 176, 177, 178, 179, 181, 184, 185, 187, 188, 190, 192, 194, 200, 202, 204, 206, 207, 210, 211, 212, 213, 214, 216, 220, 222, 237, 238, 239, 240, 242, 243, 245, 247, 248, 251, 252, 253, 254, 255, 256, 258, 261, 264; C.I. Pigment Blue 1, 2, 9, 10, 14, 15:1, 15:2, 15:3, 15:4, 15:6, 15, 16, 18, 19, 24:1, 25, 56, 60, 61, 62, 63, 64, 66, bridged aluminum phthalocyanine pigments; C.I. Pigment Black 1, 7, 20, 31, 32; C. I. Pigment Orange 1, 2, 5, 6, 13, 15, 16, 17, 17:1, 19, 22, 24, 31, 34, 36, 38, 40, 43, 44, 46, 48, 49, 51, 59, 60, 61, 62, 64, 65, 66, 67, 68, 69; C.I. Pigment Green 1, 2, 4, 7, 8, 10, 36, 45; C.I. Pigment Violet 1, 2, 3, 5:1, 13, 19, 23, 25, 27, 29, 31, 32, 37, 39, 42, 44, 50; or C.I. Pigment Brown 1, 5, 22, 23, 25, 38, 41, 42.

Ink compositions, both pigment-based and clear, useful in the invention also comprise a humectant in order to achieve reliable firing at high frequency with low velocity variability. Representative examples of humectants which may be employed in the present invention include: (1) triols, such as; glycerol, 1,2,6-hexanetriol, 2-ethyl-2-hydroxymethyl-propane diol, trimethylolpropane, alkoxlated triols, alkoxylated pentaerythritols, saccharides, and sugar alcohols; and (2) diols, such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyalkylene glycols having four or more alkylene oxide groups, 1,3-propane diol, 1,2-butane diol, 1,3-butane diol, 1,4-butane diol, 1,2-pentane diol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexane diol, 2-methyl-2,4-pentanediol, 1,2-heptane diol, 1,7-hexane diol, 2-ethyl-1,3-hexane diol, 1,2-octane diol, 2,2,4-trimethyl-1,3-pentane diol, 1,8-octane diol; and thioglycol or a mixture thereof.

Desirable humectants are polyhydric alcohols having three or more hydroxyl groups. A particularly useful humectant is glycerol. Typical aqueous-based ink compositions useful in the invention may contain 5-20 weight percent humectant(s), especially from 6-15% humectant, most desirably from about 6-10% humectant. Inks comprising humectants having the aforementioned viscosity and concentration ranges are ideal for maintaining ink viscosities in an acceptable range for high speed firing from a thermal ink jet printhead with low variability in firing velocity.

The ink compositions of the present may also include a water miscible co-solvent or penetrant. Representative examples of co-solvents used in the aqueous-based ink compositions include: (1) alcohols, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, iso-butyl alcohol, furfuryl alcohol, and tetrahydrofurfuryl alcohol; (2) lower mono- and di-alkyl ethers derived from the polyhydric alcohols; such as ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether acetate, diethylene glycol monomethyl ether, and diethylene glycol monobutyl ether acetate; (3) nitrogen-containing compounds, such as urea, 2-pyrrolidinone, N-methyl-2-pyrrolidinone, and 1,3-dimethyl-2-imidazolidinone; and (4) sulfur-containing compounds, such as 2,2′-thiodiethanol, dimethyl sulfoxide, and tetramethylene sulfone. Typical aqueous-based ink compositions useful in the invention may contain 2-10 weight percent co-solvent(s).

The pigment-based and clear ink compositions of the present invention may also contain a water-soluble acrylic polymer comprising carboxylic acid groups. The term “water-soluble” is defined herein as when the polymer is dissolved in water and when the polymer is at least partially neutralized with an inorganic monovalent base the resultant solution is visually clear.

The monomers for the water-soluble acrylic polymer of this invention can be selected from methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate, hexyl acrylate, n-octyl acrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, nonyl acrylate, benzyl methacrylate, 2-hydroxypropyl methacrylate, acrylonitrile, methacrylonitrile, vinyl acetate, vinyl propionate, vinylidene chloride, vinyl chloride, styrene, α-methyl styrene, t-butyl styrene, vinyl toluene, butadiene, isoprene, N,N-dimethyl acrylamide, acrylic acid, methacrylic acid, chloromethacrylic acid, maleic acid, and derivatives thereof. Examples of suitable monomers include allyl compounds such as allyl esters (e.g., allyl acetate, allyl caproate, etc.); vinyl ethers (e.g., methyl vinyl ether, butyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinyl ether, chloroethyl vinyl ether, 1-methyl-2,2-dimethylpropyl vinyl ether, hydroxyethyl vinyl ether, diethylene glycol vinyl ether, dimethylaminoethyl vinyl ether, butylaminoethyl vinyl ether, benzyl vinyl ether, tetrahydrofurfuryl vinyl ether, etc.); vinyl esters (such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl dimethyl propionate, vinyl ethyl butyrate, vinyl chloroacetate, vinyl dichloroacetate, vinyl methoxyacetate, vinyl phenyl acetate, vinyl acetoacetate, etc.); vinyl heterocyclic compounds (such as N-vinyl oxazolidone, N-vinylimidazole, N-vinylpyrrolidone, N-vinylcarbazole, vinyl thiophene, N-vinylethyl acetamide, etc.); styrenes (e.g., styrene, divinylbenzene, methylstyrene, dimethylstyrene, ethylstyrene, isopropylstyrene, sodium styrenesulfonate, potassium styrenesulfinate, butylstyrene, hexylstyrene, cyclohexylstyrene, benzylstyrene, chloromethylstyrene, trifluoromethylstyrene, acetoxymethylstyrene, acetoxystyrene, vinylphenol, (t-butoxycarbonyloxy) styrene, methoxystyrene, 4-methoxy-3-methylstyrene, dimethoxystyrene, chlorostyrene, dichlorostyrene, trichlorostyrene, bromostyrene, iodostyrene, fluorostyrene, methyl vinylbenzoate ester, vinylbenzoic acid, etc.); crotonic acids (such as crotonic acid, crotonic acid amide, crotonate esters (e.g., butyl crotonate, etc.)); vinyl ketones (e.g., methyl vinyl ketone, etc ); olefins (e.g., dicyclopentadiene, ethylene, propylene, 1-butene, 5,5-dimethyl-1-octene, etc.); itaconic acids and esters (e.g., itaconic acid, methyl itaconate, etc.), other acids such as sorbic acid, cinnamic acid, methyl sorbate, citraconic acid, chloroacrylic acid mesaconic acid, maleic acid, fumaric acid, and ethacrylic acid; halogenated olefins (e.g., vinyl chloride, vinylidene chloride, etc.); unsaturated nitriles (e.g., acrylonitrile, etc.); acrylic or methacrylic acids and esters (such as acrylic acid, methyl acrylate, methacrylic acid, methyl methacrylate, ethyl acrylate, butyl acrylate, butyl methacrylate, 2-hydroxyethyl methacrylate, 2-acetoacetoxyethyl methacrylate, sodium-2-sulfoethyl acrylate, 2aminoethylmethacrylate hydrochloride, glycidyl methacrylate, ethylene glycol dimethacrylate, etc.); and acrylamides and methacrylamides (such as acrylamide, methacrylamide, N-methylacrylamide, N,N-dimethylacrylamide, N-isopropylacrylamide, N-s-butylacrylamide, N-t-butylacrylamide, N-cyclohexylacrylamide, N-(3-aminopropyl)methacrylamide hydrochloride, N-(3-dimethylaminopropyl)methacrylamide hydrochloride, N,N-dipropylacrylamide, N-(1,1-dimethyl-3-oxobutyl)acrylamide, N-(1,1,2-trimethylpropyl) acrylamide, N-(1,1,3,3-tetramethylbutyl)acrylamide, N-(1-phthalamidomethyl)acrylamide, sodium N-(1,1-dimethyl-2-sulfoethyl)acrylamide, N-butylacrylamide, N-(1,1-dimethyl-3-oxobutyl)acrylamide, N-(2-carboxyethyl)acrylamide, 3-acrylamido-3-methylbutanoic acid, etc.).

The water-soluble acrylic polymer can be prepared by emulsion polymerization, solution polymerization, or bulk polymerization technique well known in the art. Typically, the water-soluble acrylic polymer has a weight average molecular weight of less than 20,000. Desirably, the polymer has a sufficient number of acid groups such that the acid number of the polymer is greater than 115.

The acid groups on the acrylic polymers are at least partially neutralized (converted into salts) using monovalent inorganic bases, typically aqueous alkaline metal hydroxides, selected from; potassium hydroxide, sodium hydroxide, rubidium hydroxide or lithium hydroxide. In a one particularly useful embodiment, at least 70 percent of the available acid groups on the polymer are converted into salts using monovalent inorganic base, more desirably at least 90% of the available acid groups are converted. Monovalent inorganic bases are highly preferred over organic bases such as amines as the neutralizing agents for the acrylic polymers since inks containing acrylic polymers neutralized with organic amines show very poor jetting performance in a thermal ink jet printhead.

Acrylic polymers which may be employed in the present invention are exemplified by those disclosed in U.S. Pat. No. 6,866,379, which is incorporated herein in their entirety by reference. Specific examples of preferred water-soluble polymers useful in the present invention are copolymers prepared from at least one hydrophilic monomer that is an acrylic acid or methacrylic acid monomer, or combinations thereof. Preferably, the hydrophilic monomer is methacrylic acid.

Water-soluble polymers particularly useful in the present invention are copolymers prepared from at least one hydrophobic monomer that is an (meth)acrylic acid ester. Examples of hydrophobic monomers include, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, lauryl(methacrylate), stearyl (meth)acrylate, benzyl (meth)acrylate, phenyl (meth)acrylate, or combinations thereof. Preferred hydrophobic monomers are benzyl (meth)acrylate.

The water-soluble polymer may also be a styrene-acrylic copolymer comprising a mixture of vinyl or unsaturated monomers, including at least one styrenic monomer and at least one acrylic monomer, at least one of which monomers has an acid or acid-providing group. Such polymers are disclosed in, for example, U.S. Pat. Nos. 4,529,787; 4,358,573; 4,522,992; and 4,546,160; the disclosures of which are incorporated herein by reference. Preferred polymers include, for example, styrene-acrylic acid, styrene-acrylic acid-alkyl acrylate, styrene-maleic acid, styrene-maleic acid-alkyl acrylate, styrene-methacrylic acid, styrene-methacrylic acid-alkyl acrylate, and styrene-maleic acid half ester, wherein each type of monomer may correspond to one or more particular monomers. Examples of preferred polymers include but are not limited to styrene-acrylic acid copolymer, (3-methyl styrene)-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-butyl acrylate-acrylic acid terpolymer, styrene-butyl methacrylate-acrylic acid terpolymer, styrene-methyl methacrylate-acrylic acid terpolymer, styrene-butyl acrylate-ethyl acrylate-acrylic acid tetrapolymer, and styrene-(α-methylstyrene)-butyl acrylate-acrylic acid tetrapolymer.

The water-soluble acrylic polymer is not limited in the arrangement of the monomers comprising the copolymer. The arrangement of monomers may be totally random, or they may be arranged in blocks such as AB or ABA wherein, A is the hydrophobic monomer and B is the hydrophilic monomer. In addition, the polymer make take the form of a random terpolymer or an ABC triblock wherein, at least one of the A, B, and C blocks is chosen to be the hydrophilic monomer and the remaining blocks are hydrophobic blocks dissimilar from one another.

The water-soluble acrylic polymer useful in the pigment-based inks of the present invention is typically present in the pigment based ink jet ink at a concentration of greater than 0.6 weight percent based on the total weight of the ink. In a useful embodiment of the present invention the ink composition comprises a polyurethane described above and a water-soluble polymer described above wherein, the ratio of total amount of polyurethane and acrylic polymer(s) to pigment is from 0.5 to 1.5 and the ratio of polyurethane polymer to acrylic polymer is from 0.5 to 2. The use of acrylic polymer in the clear ink is optional.

In another useful embodiment, the components of the ink composition are selected such that the ink viscosity is typically less than 3.5 centapoise at 25 degrees Celsius, more suitably less than about 3.0 and desirably less than 2.0. Ink compositions defined by these desirable embodiments are capable of achieving high firing frequencies with low variability for a large number of firing events.

Surfactants may be added to adjust the surface tension of the ink to an appropriate level. In a particular embodiment, relative dynamic and static surface tensions of various pigment based inks and clear protective ink of an ink set may be controlled as described in copending, commonly assigned U.S. Ser. No. 60/892,176, filed Feb. 28, 2007, the disclosure of which is incorporated by reference herein, to control intercolor bleed between the inks. The surfactants may be anionic, cationic, amphoteric, or nonionic and used at levels of 0.01 to 5% of the ink composition. Examples of suitable nonionic surfactants include, linear or secondary alcohol ethoxylates (such as the TERGITOL® 15-S and TERGITOL® TMN series available from Union Carbide and the BRIJ® series from Uniquema), ethoxylated alkyl phenols (such as the TRITON® series from Union Carbide), fluoro surfactants (such as the ZONYLS® from DuPont; and the FLURADS® from 3M), fatty acid ethoxylates, fatty amide ethoxylates, ethoxylated and propoxylated block copolymers (such as the PLURONIC® and TETRONIC® series from BASF, ethoxylated and propoxylated silicone based surfactants (such as the SILWET® series from CK Witco), alkyl polyglycosides (such as the GLUCOPONS® from Cognis), and acetylenic polyethylene oxide surfactants (such as the Surfynols from Air Products, Inc.).

Examples of anionic surfactants include carboxylated (such as ether carboxylates and sulfosuccinates), sulfated (such as sodium dodecyl sulfate), sulfonated (such as dodecyl benzene sulfonate, alpha olefin sulfonates, alkyl diphenyl oxide disulfonates, fatty acid taurates, and alkyl naphthalene sulfonates), phosphated (such as phosphated esters of alkyl and aryl alcohols, including the STRODEX® series from Dexter Chemical), phosphonated and amine oxide surfactants, and anionic fluorinated surfactants. Examples of amphoteric surfactants include betaines, sultaines, and aminopropionates. Examples of cationic surfactants include quaternary ammonium compounds, cationic amine oxides, ethoxylated fatty amines, and imidazoline surfactants. Additional examples of the above surfactants are described in “McCutcheon's Emulsifiers and Detergents,” 1995, North American Editor.”

A biocide (0.01-1.0% by weight) may also be added to prevent unwanted microbial growth which may occur in the ink over time. A preferred biocide for the inks employed in the present invention is PROXEL® GXL (Zeneca Colours Co.) at a concentration of 0.05-0.1% by weight or/and KORDEK® (Rohm and Haas Co.) at a concentration of 0.05-0.1% by weight (based on 100% active ingredient). Additional additives which may optionally be present in an ink jet ink composition include thickeners, conductivity enhancing agents, anti-kogation agents, drying agents, waterfast agents, dye solubilizers, chelating agents, binders, light stabilizers, viscosifiers, buffering agents, anti-mold agents, anti-curl agents, stabilizers, and defoamers.

The pH of the aqueous ink compositions of the invention may be adjusted by the addition of organic or inorganic acids or bases. Inorganic bases are preferred; however, small amounts of organic bases, such as triethanolamine, may be used to adjust the pH of the ink. Useful inks may have a preferred pH of from about 4 to 10, depending upon the type of pigment being used. Preferably, the pH of the present ink is from 6 to 9, more preferably from 7.5 to 8.5.

The invention is summarized above. Inkjet printing systems useful in the invention comprise a printer, at least one ink, and an image recording element, typically a sheet (herein also “media”), suitable for receiving ink from an inkjet printer. The method of the invention employs the inkjet printer of the invention to provide an image on media. Inkjet printing is a non-impact method for producing printed images by the deposition of ink droplets in a pixel-by-pixel manner to an image-recording element in response to digital data signals. There are various methods that may be utilized to control the deposition of ink droplets on the image-recording element to yield the desired printed image. In one process, known as drop-on-demand inkjet, individual ink droplets are projected as needed onto the image-recording element to form the desired printed image. Common methods of controlling the projection of ink droplets in drop-on-demand printing include piezoelectric transducers, thermal bubble formation or an actuator that is made to move.

Drop-on-demand (DOD) liquid emission devices have been known as ink printing devices in ink jet printing systems for many years. Early devices were based on piezoelectric actuators such as are disclosed in U.S. Pat. Nos. 3,946,398 and 3,747,120. A currently popular form of ink jet printing, thermal ink jet (or “thermal bubble jet”), uses electrically resistive heaters to generate vapor bubbles which cause drop emission, as is discussed in U.S. Pat. No. 4,296,421. In another process, known as continuous inkjet, a continuous stream of droplets is generated, a portion of which are deflected in an image-wise manner onto the surface of the image-recording element, while un-imaged droplets are caught and returned to an ink sump. Continuous inkjet printers are disclosed in U.S. Pat. Nos. 6,588,888; 6,554,410; 6,682,182; 6,793,328; 6,866,370; 6,575,566; and 6,517,197.

The FIGURE shows one schematic example of an inkjet printer 10 that includes a protective cover 40 for the internal components of the printer. The printer contains a recording media supply 20 in a tray. The printer includes one or more ink tanks 18 (shown here as having four inks) that supply ink to a printhead 30. The printhead 30 and ink tanks 18 are mounted on a carriage 100. The printer includes a source of image data 12 that provides signals that are interpreted by a controller (not shown) as being commands to eject drops of ink from the printhead 30. Printheads may be integral with the ink tanks or separate. Exemplary printheads are described in U.S. Pat. No.7,350,902. In a typical printing operation a media sheet travels from the recording media supply 20 in a media supply tray to a region where the printhead 30 deposits droplets of ink onto the media sheet. The printed media collection 22 is accumulated in an output tray.

The following examples illustrate, but do not limit, the utility of the present invention.

EXAMPLES Polyurethane Binders Used in the Examples

-   Comparative Polyurethane PU-1 A polyurethane was made by     polymerizing 39% isophorone diisocyanate, 24% 2,2-bis(hydroxymethyl)     propionic acid (DMPA), and 37% of a 2000 Mw polytetrahydrofuran     polyol. The resulting 100 acid number polyurethane had a weight     average molecular weight of 20,400 and 95% of the acid groups were     neutralized with potassium hydroxide. -   Comparative Polyurethane PU-2 A polyurethane was made by     polymerizing 39% isophorone diisocyanate, 24% 2,2-bis(hydroxymethyl)     propionic acid (DMPA), and 37% of a 2000 Mw polytetrahydrofuran     polyol. The resulting 100 acid number polyurethane had a weight     average molecular weight of 10,000 and 95% of the acid groups were     neutralized with potassium hydroxide. -   Inventive Polyurethane PU-3 A polyurethane was made by polymerizing     52% isophorone diisocyanate, 24% 2,2-bis(hydroxymethyl) propionic     acid (DMPA), and 24% of Polyfox T fluorinated polyol with a Mw of     1300 available from Omnova Solutions. The resulting 100 acid number     polyurethane had a weight average molecular weight of 21,000 and 95%     of the acid groups were neutralized with potassium hydroxide. -   Inventive Polyurethane PU-4 A polyurethane was made by polymerizing     43% isophorone diisocyanate, 24% 2,2-bis(hydroxymethyl) propionic     acid (DMPA), and 33% of POLYFOX® 636 fluorinated polyol (believed to     be a fluorinated diol of structure II where n=6) available from     Omnova Solutions. The resulting 100 acid number polyurethane had a     weight average molecular weight of 10,000 and 95% of the acid groups     were neutralized with potassium hydroxide. -   Inventive Polyurethane PU-5 A polyurethane was made by polymerizing     52% isophorone diisocyanate, 24% 2,2-bis(hydroxymethyl) propionic     acid (DMPA), and 21.4% Polyfox T fluorinated polyol with a Mw of     1300 available from Omnova, and 2.4% of a 3000 Mw     polydimethylsiloxane with amine terminating groups. The resulting     100 acid number polyurethane had a weight average molecular weight     of 28,150 and 95% of the acid groups were neutralized with potassium     hydroxide. -   Inventive Polyurethane PU-6 A polyurethane was made by polymerizing     52% isophorone diisocyanate, 24% 2,2-bis(hydroxymethyl) propionic     acid (DMPA), 19.3% Polyfox T fluorinated polyol with a Mw of 1300     available from Omnova, and 4.7% of a 3000 Mw polydimethylsiloxane     with amine terminating groups. The resulting 100 acid number     polyurethane had a weight average molecular weight of 45,900 and 95%     of the acid groups were neutralized with potassium hydroxide. -   Inventive Polyurethane PU-7 A polyurethane was made by polymerizing     52% isophorone diisocyanate, 24% 2,2-bis(hydroxymethyl) propionic     acid (DMPA), 21% of Polyfox T fluorinated polyol with a Mw of 1300     available from Omnova Solutions, and 3% of a 2000 Mw     polytetrahydrofuran polyol (Terathane). The resulting 100 acid     number polyurethane a weight average molecular weight of 17,500 and     95% of the acid groups were neutralized with potassium hydroxide. -   Inventive Polyurethane PU-8 A polyurethane was made by polymerizing     52% isophorone diisocyanate, 24% 2,2-bis(hydroxymethyl) propionic     acid (DMPA), 19% of Polyfox T fluorinated polyol with a Mw of 1300     available from Omnova Solutions, and 5% of a 2000 Mw     polytetrahydrofuran polyol (Terathane). The resulting 100 acid     number polyurethane had a weight average molecular weight of 15,200     and 95% of the acid groups were neutralized with potassium     hydroxide. -   Inventive Polyurethane PU-9 A polyurethane was made by polymerizing     52.45% isophorone diisocyanate, 23.94% 2,2-bis(hydroxymethyl)     propionic acid (DMPA), 23.37% of Polyfox T fluorinated polyol with a     Mw of 1300 available from Omnova Solutions, and 0.24% of a 2000 Mw     polytetrahydrofuran polyol (Terathane). The resulting 100 acid     number polyurethane had a weight average molecular weight of 22,400     and 95% of the acid groups were neutralized with potassium     hydroxide. -   Inventive Polyurethane PU-10 A polyurethane was made by polymerizing     42% isophorone diisocyanate, 24% 2,2-bis(hydroxymethyl) propionic     acid (DMPA), 10% of FMS-9922 a silanol terminated     polytrifluoropropylmethylsiloxane with a Mw of (800-1200) available     from Gelest, Inc., and 24% of a 2000 Mw polytetrahydrofuran polyol     (Terathane). The resulting 100 acid number polyurethane had a weight     average molecular weight of 40,300 and 95% of the acid groups were     neutralized with potassium hydroxide.

Weight Average Molecular Weight

Samples of the polyurethanes were analyzed using size-exclusion chromatography (SEC) at 35.0 C in tetrahydrofuran (THF) containing 1.0% formic acid. The column set consists of three 7.5 mm×300 mm Plgel mixed-B columns from Polymer Laboratories (Varian, Inc.), calibrated with narrow-molecular-weight distribution polystyrene standards.

Preparation of Pigment Dispersions

-   C-1 A dispersion of cyan pigment PB15:3 with an acrylic copolymer     made from 37 wt % benzyl methacrylate, 30 wt %     n-octadecylmethacrylate, and 33 wt % methacrylic acid as the pigment     dispersant. The dispersant having 90% of the acid groups neutralized     with potassium hydroxide. -   M-1 A dispersion of magenta pigment Ciba Cromophtal Jet Magenta     PR2BC with an acrylic copolymer made from 37 wt % benzyl     methacrylate, 30 wt % n-octadecylmethacrylate, and 33 wt %     methacrylic acid as the pigment dispersant. The dispersant having     90% of the acid groups neutralized with potassium hydroxide. -   Y-1 A dispersion of yellow pigment PY74 an acrylic copolymer 37 wt %     benzyl methacrylate, 30 wt % n-octadecylmethacrylate, 33 wt %     methacrylic acid, an acrylic copolymer made from 77.5 wt % benzyl     methacrylate, and 22.5 wt % methacrylic acid, both polymers having     90% of the acid groups neutralized with potassium hydroxide. -   K-1 A dispersion of carbon black pigment Cabot Black Pearls 880 with     an acrylic copolymer made from 37 wt % benzyl methacrylate, 30 wt %     n-octadecylmethacrylate, and 33 wt % methacrylic acid as the pigment     dispersant. The dispersant having 90% of the acid groups neutralized     with potassium hydroxide.

Pigment Ink Preparations

Into an approximately 150 ml high density polyethylene bottle with magnetic stirring, the following components were added in order: high purity water, 0.02 wt % of the biocide Kordek MLX, 3 wt % of glycerol, 4 wt % of 2-pyrrolidinone, 2 wt % of 1-(2-hydroxyethyl)-2-pyrrolidinone, 3 wt % of 1,2-hexanediol, 0.1 wt % of the Strodex PK90 surfactant, and 1.2 wt % of polyurethane from an approximately 25 to 30 wt % aqueous solution. Pigment dispersion was added as described below in Table 1. 1N KOH was added if necessary to adjust pH to about 8.3-8.5. The resulting 125g of ink was stirred for at least an hour and filtered with a 1.0 um disk filter.

TABLE 1 Pigment Concentrations in Colored Inks Ink Color Pigment and Level Cyan 2.2 wt % C-1 Magenta  3.5% M-1 Yellow  2.75% Y-1 Black 1.675% K-1, 0.45% C-1, 0.375% M-1

Clear Ink Preparations

Into an approximately 150 ml high density polyethylene bottle with magnetic stirring, the following components were added in order: high purity water, 0.02 wt % of the biocide Kordek MLX, 12 wt % of glycerol, 6 wt % of ethylene glycol, 2 wt % of 1,2-pentanediol, 0.75 wt % of the Tergitol 15-S-5 surfactant, 1.6 wt % total of one or more polyurethanes (from an approximately 25 to 30 wt % aqueous solution), 0.8% of an acrylic copolymer made from 67 wt % benzyl methacrylate, and 33% methacrylic acid. 1N KOH was added if necessary to adjust pH to about 8.3-8.5. The resulting 125 g of ink were stirred for at least an hour and filtered with a 1.0 um disk filter.

Preparation of Ink Sets

Inks sets comprising cyan, magenta, yellow, black, and clear inks prepared with the same experimental polyurethane polymers were assembled and used to fill ink cartridges for printing in a Kodak 5100 All-in-One inkjet printer. The polyurethanes used for each ink set are described below in Table 2.

TABLE 2 Definition of Ink Sets Ink Set Polyurethane in Pigment and Clear Inks S-1 comparative PU-1: non-fluorinated polyurethane S-2 inventive PU-3: 21k Mw fluorinated polyurethane S-3 inventive PU-4: 10k Mw fluorinated polyurethane S-4 inventive 1:1 mixture of PU-1 and PU-3 S-5 inventive 1:1 mixture of PU-1 and PU-4 S-6 inventive 11:1 mixture of PU-3 and PU-1 S-7 inventive 11:1 mixture of PU-5 and PU-1 S-8 inventive 1:1 mixture of PU-6 and PU-1 S-9 inventive PU-10: mixture of soft segments

Jetting of Magenta Ink Examples

A series of magenta pigment inks prepared according to the pigment ink formulation above were prepared using polyurethanes PU-1, PU-2, PU-3, and PU-4. Each ink was loaded directly into a thermal printhead with 3 pL nozzles. At a voltages of 12% above the threshold voltage for the ink to begin firing, the transit time for each drop to travel 0.3 mm from the nozzle plate was measured for 250 drops from 10 different nozzles firing at 11.7, 12.35, and 13.0 kHz. The mean velocity and root mean squared variation were calculated from all of the individual velocity measurements and are shown in Table 3.

TABLE 3 Ink Formulation and Jetting Performance with Magenta Pigment Jetting Jetting Percent Frequency Poly- Fluoro PU velocity Velocity limit Ink urethane polyol (Mw) m/sec variation kHz I-1 PU-1 No 20,400 20.4 0.96 21.5 Comp. I-2 PU-2 No 10,000 12.7 4.01 N.A. Comp. I-3 PU-3 yes 21,000 15.9 1.16 25.6 Inv. I-4 PU-4 yes 10,000 17.4 1.16 23.1 Inv.

Ink I-2, containing the low molecular weight non-fluorinated polyurethane (PU-2), exhibits poor jetting behavior with low velocity and very high velocity variation as compared to the other inks. In contrast, the low molecular weight fluorinated polyurethane containing ink (I-4) shows excellent jetting with good velocity and low velocity variation as well as an improved frequency limit. The higher molecular weight fluorinated polyurethane based ink (I-3) also shows good jetting performance, similar to the comparative ink (I-1), but again a significantly higher frequency response limit.

Jetting of Cyan Ink Examples

-   Ink Example I-5 A cyan pigment ink was prepared according to the     following procedure. Into an approximately 150 ml high density     polyethylene bottle with magnetic stirring, the following components     were added in order: 61.03 g of high purity water, 0.26 g of a 9.5     wt % solution of the biocide Kordek MLX, 3.75 g of glycerol, 5.0 g     of 2-pyrrolidinone, 2.50 g of 1-(2-hydroxyethyl)-2-pyrrolidinone,     3.75 g of 1,2-hexanediol, 0.13 g of the Strodex PK90 surfactant,     5.09 g of a 29.46 wt % solution of polyurethane PU-1, 43.19 g of     polymerically dispersed cyan pigment PB15:3 pigment dispersion C-1     containing about 10 wt % pigment, and 0.3 g of 1N KOH to adjust pH     to about 8.3. The resulting 125 g of ink was stirred for at least an     hour and filtered with a 1.0 um disk filter. -   Ink examples I-6 through I-12 were made identically to I-5 except     for the changes in the polyurethane polymer as specified below     Table 4. The water level was adjusted to compensate for differences     in the concentration of the polymer solutions so that the total     weight of ink prepared was always 125 g.

Each ink was loaded directly into a thermal printhead with 3 pL nozzles. At a voltages of 12% above the threshold voltage for the ink to begin firing, the transit time for each drop to travel 0.3mm from the nozzle plate was measured for 250 drops from 10 different nozzles firing at 11.7, 12.35, and 13.0 kHz. The mean velocity and root mean squared variation were calculated from all of the individual velocity measurements.

TABLE 4 Ink Formulation and Jetting Performance with Cyan Pigment Jetting Percent Wt % velocity Velocity Polyurethane polyurethane in m/sec at variation at Ink Polymers the ink 12 kHz 12 kHz I-5 100% PU-3 1.2% PU-3 6.88 15.8 Comp. I-6 11:1 PU-3:PU-1 1.1% PU-3, 13.8 1.84 Inventive 0.1% PU-1 I-7 23:1 PU-3:PU-1 1.15% PU-3, 13.6 1.72 Inventive 0.05% PU-1 I-8 47:1 PU-3:PU-1 1.175% PU-3, 11.8 1.58 Inventive 0.025% PU-1 I-9 99:1 PU-3:PU-1 1.188% PU-3, 10.0 8.70 Inventive 0.012% PU-1 I-10 100% PU-7 1.2% PU-7 14.8 1.72 Inventive I-11 100% PU-8 1.2% PU-8 14.6 1.66 Inventive I-12 100% PU-9 1.2% PU-9 11.5 2.02 Inventive

Table 4 shows that some inks, such as I-5, containing polyurethanes made with only a first fluorinated polyol soft-segment can show poor jetting performance with some pigments, such as the polymerically dispersed cyan pigment PB15:3. Surprisingly, inks I-6 through I-9 show that the addition of a second non-fluorinated polyether polyurethane to an ink comprising a first fluorinated polyurethane can dramatically improve the jetting performance so that both high jetting velocity and low velocity variation are observed. The improved jetting is achieved at levels of the non-fluorinated polyurethane as low as 1% of the total polyurethane in the ink. Table 4 also shows that the jetting performance of inks containing fluorinated polyurethanes (Inks I-10, I-11 and I-12) can be significantly improved by adjusting the structure of the polyurethane to include a first soft segment comprising fluorinated groups and a second non-fluorinated soft segment. The jetting performance of fluorinated polyurethanes can be dramatically improved by the presence of as little as 0.24% non-fluorinated soft segment by weight in the polymer.

Blunt Scratch DurabilityTesting

Each ink set, S-1 through S-9, were loaded into the respective tank of a color ink cartridge suitable for printing on a Kodak 5100 All-In-One inkjet printer. The tank was loaded into the printer and a scratch test target was printed on a commercially available alumina-based glossy print media using the Kodak 5100 printer with commercially available print driver and printing modes optimized for the specific media. The test target consisted of three separate 64-patch targets made up of various color patches. One target each was scratch tested at 2, 10, and 60 minutes after print ejection using a round wire stylus with a 150 g load.

The overall scratch score was determined by examining each of the 64 image patches after scratching with the round wire stylus. If the scratch penetrated through the image such that the receiver was clearly visible the patch was scored with a 2. Scratches of this nature are easily visible and highly objectionable to a consumer. If the scratch was clearly visible under normal lighting conditions and not require any tilting of the image to view the scratch the patch was scored a 1. If a deformation of the surface was evident only after tilting (but no visible scratch was seen) the image the patch was scored a zero. Thus, the maximum worst possible abrasion resistance would result in a score of 128 and the best possible abrasion resistance would result in a score of zero. The results of the scratch test for each ink set at the three times after print ejection are tabulated below in Table 5.

TABLE 5 Results of Blunt Scratch Testing for Ink Sets S-1 through S-9 2-minute 10-minute 60-minute scratch scratch scratch score score score With With With Polyurethane clear Without clear Without clear Without Ink Set type ink clear ink ink clear ink ink clear ink S-1 PU-1 87 75 38 38 11 2 comparative No fluorination S-2 PU-3 99 60 8 3 0 1 inventive 21k Mw with fluorination S-3 PU-4 85 71 29 25 0 0 inventive 10k Mw with fluorination S-4 1:1mixture of 85 56 24 10 0 0 inventive PU-1 and PU-3 S-5 1:1 mixture of 86 61 21 5 0 0 inventive PU-1 and PU-4 S-6 11:1mixture of 86 N.A. 28 N.A. 1 N.A. inventive PU-3 and PU-1 S-7 11:1mixture of 79 N.A. 16 N.A. 0 N.A. inventive PU-5 and PU-1 S-8 11:1mixture of 94 N.A. 19 N.A. 0 N.A. inventive PU-6 and PU-1 S-9 PU-10 50 N.A 5 N.A. 2 N.A. inventive Fluorinated PDMS

The scratch test results in Table 5 show that ink sets containing fluorinated polyurethanes reduce the scratching propensity of printed images, especially at moderate drying times of 10 to 60 minutes. The improved abrasion resistance is evident both with and without the application of clear ink. Table 5 also shows that the fluorinated polyurethanes reduce scratching even at the shortest drying time of 2 minutes when the clear ink is omitted. The improved scratch performance of ink sets printed without clear ink is in part explained by the reduction in the total fluid lay down (absence of water and humectants present in clear ink) which allows for faster drying of the images.

Spur Track Visibility

A combination of targets and images with large dark regions or backgrounds were printed with a Kodak All-In-One printer having a spur wheel mechanism using the full inks sets S-1, S-2, and S-6 through S-9 described above. The visibility of the resulting spur track after printing was rated on a 0 to 5 scale where a 0 is not visible (even under examination with a 10× magnification) and a 5 is extremely visible such that the image is severely damaged and would likely be discarded. A value greater than 3 would be judged as detrimental to overall image quality. Spur track marks receiving ratings in the range of 0.5 to 3 could be detected under careful inspection, but the overall image quality would be judged as acceptable under typical viewing conditions. The results are described below in Table 6.

TABLE 6 Spur track visibility rating dark brown Polyurethane gray black reddish-brown shadow Ink Set type scale target background background background S-1 PU-1 4 4 4 4 comparative No fluorination S-2 PU-3  2* 1.5* 1.5* 1.5* inventive 21k Mw with fluorination S-6 11:1mixture of   2.5 2.5 1.5 1.5 inventive PU3 and PU1 S-7 11:1mixture of 3 2 1.5 1 inventive PU5 and PU1 S-8 11:1mixture of 2 1.5 1 0.5 inventive PU6 and PU1 S-9 PU-10 3 2.5 2.5 3 inventive Fluorinated PDMS *results may be better than expected due to lower ink deposition in dark regions caused by poor jetting of some inks such as the cyan described table 3 above.

Table 6 shows that inks sets (S-2 through S-9) made with polyurethanes containing fluorinated soft segments can dramatically improve the visibility of spur tack marks. Polyurethanes containing a mixture of a first soft segment prepared from a fluorinated polyether and a second soft segment prepared from an aminoalkyl polydimethylsiloxane can further reduce the visibility of the spur track marks.

The invention has been described with reference to a preferred embodiment; however, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention. The various patents and other publications mentioned herein are incorporated herein in their entirety by reference.

Parts List

-   10 inkjet printer -   12 image data source -   18 ink tanks -   20 recording medium supply -   22 printed media collection -   30 printhead -   40 protective cover -   100 carriage -   215 optical sensor -   302 media direction -   303 print region -   304 media direction -   313 forward direction -   320 pickup roller(s) -   322 turn roller(s) -   323 idler roller(s) -   324 discharge roller(s) -   325 star wheel(s) -   360 media supply tray -   371 media Sheet -   375 further optical sensor -   380 media output tray -   390 printed media sheet 

1. An inkjet printing system, comprising: I) an inkjet printer; II) an ink composition comprising: (a) water; (b) dispersed pigment particles; (c) a humectant; and (d) a fluorinated polyurethane additive which is different from any pigment polymeric dispersant in the ink, the additive having a weight average molecular weight of at least 10,000 daltons.
 2. The inkjet printing system of claim 1 wherein the pigment particles are self-dispersing.
 3. The inkjet printing system of claim 1 wherein the pigment particles are dispersed by a surfactant.
 4. The inkjet printing system of claim 1 wherein the pigment particles are dispersed by a polymeric dispersant.
 5. An aqueous ink composition comprising; (a) water, (b) pigment particles dispersed with a surfactant or self dispersing without the need for a dispersant, (c) at least one humectant, and (d) at least one fluorinated polyurethane additive which is different from any pigment dispersant in the ink, having a weight average molecular weight of at least 10,000.
 6. The ink composition of claim 5, wherein the fluorinated polyurethane additive comprises at least one first soft segment comprising fluorinated side chains.
 7. The ink composition of claim 6, wherein the fluorinated side chain is a fluoroalkyl group.
 8. The ink composition of claim 7, wherein the fluoralkyl group comprises from 2 to 6 carbons.
 9. The ink composition of claim 6, wherein the fluorinated side chain is a fluorinated polyether.
 10. The ink composition of claim 9, wherein the fluorinated polyether side chain comprises from 2 to 6 carbons.
 11. The ink composition of claim 6, wherein the first soft segment further comprises siloxane groups.
 12. The ink composition of claim 5, wherein the at least one first soft segment is present in the polymer at between 2% and 30% by weight of the total polymer.
 13. The ink composition of claim 5, wherein the first soft segment is present in the polymer at between 5% and 20% by weight of the total polymer.
 14. The ink composition of claim 5, wherein the polyurethane additive further comprises at least one non-fluorinated second soft segment comprising polyether, polyester, polycarbonate or polydimethylsiloxane groups.
 15. The ink composition of claim 14, wherein the at least one second soft segment is present at between 1% and 30% by weight of the total polymer.
 16. The ink composition of claim 14, wherein the at least one second soft segment is present at between 1% and 20% by weight of the total polymer.
 17. The ink composition of claim 14, wherein the at least one second soft segment is present at between 1% and 10% by weight of the total polymer.
 18. The ink composition of claim 14, wherein the at least one second soft segment comprises tetramethylene oxide groups.
 19. The ink composition of claim 14, wherein the first soft segment comprises polyfluoroalkylmethylsiloxane groups and the second soft segment comprises polyether groups.
 20. The ink composition of claim 14, wherein the first soft segment comprises fluorinated polyether groups and the second soft segment comprises polyether groups.
 21. The ink composition of claim 5, further comprising a second non-fluorinated polyurethane additive which is distinct from the dispersant, wherein the second polyurethane additive comprises polyether groups.
 22. The ink composition of claim 21, wherein the weight ratio of the fluorinated polyurethane additive to the second non-fluorinated polyurethane additive is from 10:1to 100:1.
 23. The ink composition of claim 5, wherein the fluorinated polyurethane additive has an acid number of greater than or equal to
 20. 24. The ink composition of claim 23, wherein the fluorinated polyurethane has an acid number from 60 to
 150. 25. An ink set comprising two or more pigmented ink compositions each according to claim 5, wherein at least two of such ink compositions comprise different colored pigment particles.
 26. An ink set according to claim 25, further comprising an aqueous clear ink composition comprising; (a) at least one fluorinated polyurethane, having a weight average molecular weight of at least 10,000 daltons, and (b) at least one humectant.
 27. A method for printing an inkjet image comprising: I) providing an aqueous inkjet ink comprising: (a) water, (b) pigment particles dispersed with a surfactant or self dispersing without the need for a dispersant, (c) at least one humectant, and (d) at least one fluorinated polyurethane additive, which is different from any pigment dispersant, having a weight average molecular weight of at least 10,000 daltons; and II) jetting the inkjet ink in the form of ink drops onto the recording medium to form a printed image. 